U.S. patent application number 12/449019 was filed with the patent office on 2010-01-07 for composite magnetic body, method of manufacturing the same, circuit board using the same, and electronic apparatus using the same.
Invention is credited to Nobuhiro Hidaka, Masayuki Ishizuka, Tadahiro Ohmi, Yasushi Shirakata, Akinobu Teramoto.
Application Number | 20100000769 12/449019 |
Document ID | / |
Family ID | 39644466 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100000769 |
Kind Code |
A1 |
Ohmi; Tadahiro ; et
al. |
January 7, 2010 |
COMPOSITE MAGNETIC BODY, METHOD OF MANUFACTURING THE SAME, CIRCUIT
BOARD USING THE SAME, AND ELECTRONIC APPARATUS USING THE SAME
Abstract
There are provided a composite magnetic body exhibiting a
sufficiently low magnetic loss at frequencies of several hundreds
of megahertz to several gigahertz, and a method of manufacturing
the same. The composite magnetic body contains a magnetic powder
dispersed in an insulating material. The magnetic powder is in a
spherical shape or an elliptic shape. The composite magnetic body
has any one of the following characteristics (a) to (c): (a) the
relative magnetic permeability .mu.r is larger than 1 and the loss
tangent tan .delta. is 0.1 or less, at a frequency of 1 GHz or 500
MHz; (b) the real part .mu.r' of the complex permeability is more
than 10 and the loss tangent tan .delta. is 0.3 or less, at a
frequency of 1.2 GHz or less; and (c) the real part .mu.r' of the
complex permeability is more than 1 at a frequency of 4 GHz or
less, and the loss tangent tan .delta. is 0.1 or less at a
frequency of 1 GHz or less.
Inventors: |
Ohmi; Tadahiro; (Miyagi,
JP) ; Teramoto; Akinobu; (Miyagi, JP) ;
Ishizuka; Masayuki; (Tokyo, JP) ; Hidaka;
Nobuhiro; (Tokyo, JP) ; Shirakata; Yasushi;
(Tokyo, JP) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Family ID: |
39644466 |
Appl. No.: |
12/449019 |
Filed: |
January 22, 2008 |
PCT Filed: |
January 22, 2008 |
PCT NO: |
PCT/JP2008/050821 |
371 Date: |
July 21, 2009 |
Current U.S.
Class: |
174/255 ;
252/62.51R; 252/62.55; 252/62.56; 427/128; 427/132 |
Current CPC
Class: |
H01F 1/26 20130101; H01F
41/0246 20130101; H05K 1/0233 20130101; H01F 1/37 20130101 |
Class at
Publication: |
174/255 ;
252/62.51R; 252/62.55; 252/62.56; 427/132; 427/128 |
International
Class: |
H01F 1/01 20060101
H01F001/01; H01F 1/04 20060101 H01F001/04; B05D 5/12 20060101
B05D005/12; H05K 1/03 20060101 H05K001/03 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 23, 2007 |
JP |
2007-012092 |
Apr 13, 2007 |
JP |
2007-105496 |
Jun 12, 2007 |
JP |
2007-154751 |
Claims
1. A composite magnetic body comprising a magnetic powder dispersed
in an insulating material, the magnetic powder being in a spherical
shape or an elliptic shape, wherein the composite magnetic body has
any one of the following characteristics (a) to (C): (a) the
relative magnetic permeability .mu.r is larger than 1 and the loss
tangent tan 6 is 0.1 or less, at a frequency of 1 GHz or 500 MHz;
(b) the real part .mu.r' of the complex permeability is more than
10 and the loss tangent tan .delta. is 0.3 or less, at a frequency
of 1.2 GHz or less; and (c) the real part .mu.r' of the complex
permeability is more than 1 at a frequency of 4 GHz or less, and
the loss tangent tan 6 is 0.1 or less at a frequency of 1 GHz or
less.
2. The composite magnetic body according to claim 1, wherein the
real part .mu.r' of the complex permittivity of the composite
magnetic body is 10 or more at a frequency of 1 GHz or less.
3. The composite magnetic body according to claim 1, wherein the
real part .di-elect cons.r' of the complex permittivity of the
composite magnetic body is 10 or less at a frequency of 1 GHz or
less.
4. The composite magnetic body according to claim 1, wherein the
insulating material contains 10% to 95% by volume of the magnetic
powder.
5. The composite magnetic body according to claim 1, wherein the
magnetic powder is easily plastic-deformed in the direction of an
axis of easy magnetization by applying a mechanical stress.
6. The composite magnetic body according to claim 1, wherein the
magnetic powder has a particle size of 0.01 to 10 .mu.m.
7. The composite magnetic body according to claim 1, wherein the
magnetic powder is in an elliptic shape having a thickness of 0.01
to 1 .mu.m, a length of 0.02 to 10 .mu.m and an aspect ratio
(length/thickness) of 2 or more.
8. The composite magnetic body according to claim 7, wherein the
elliptic magnetic powder is formed by mechanically deforming the
spherical magnetic powder into an elliptic shape in the step of
mixing the magnetic powder to a dispersion solvent.
9. The composite magnetic body according to claim 7, wherein the
elliptic magnetic powder is aligned in a specific direction in the
insulating material.
10. The composite magnetic body according to claim 7, wherein
specific planes of the crystals constituting the elliptic magnetic
powder are oriented in the specific direction of the elliptic
magnetic powder.
11. The composite magnetic body according to claim 7, wherein the
longer axis direction of the elliptic magnetic powder coincides
with the axis of easy magnetization.
12. The composite magnetic body according to claim 1, wherein the
material of the magnetic powder is one selected from the group
consisting of nickel (Ni), Permalloy (Fe--Ni alloy), and Permalloy
(Fe--Ni alloy) containing at least one metal element selected from
the group consisting of aluminum (Al), chromium (Cr), manganese
(Mn), cobalt (Co), copper (Cu), zinc (Zn), niobium (Nb), molybdenum
(Mo), indium (In), and tin (Sn).
13. The composite magnetic body according to claim 12, wherein the
metal element content is 0.1% to 90% by weight in the magnetic
powder.
14. The composite magnetic body according to claim 1, wherein the
magnetic powder is an iron-based metal magnetic powder or a metal
oxide magnetic powder.
15. The composite magnetic body according to claim 14, wherein the
material of the iron-based metal magnetic powder is at least one
selected from the group consisting of iron (Fe), iron (Fe)-silicon
(Si)-based alloy, iron (Fe)-nitrogen (N)-based alloy, iron
(Fe)-carbon (C)-based alloy, iron (Fe)-boron (B)-based alloy, iron
(Fe)-phosphorus (P)-based alloy, iron (Fe)-aluminum (Al)-based
alloy, and iron (Fe)-aluminum (Al)-silicon (Si)-based alloy.
16. The composite magnetic body according to claim 15, wherein the
material of the iron-based metal magnetic powder contains at least
one metal element selected from the group consisting of titanium
(Ti), vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co),
copper (Cu), zinc (Zn), niobium (Nb), molybdenum (Mo), indium (In),
and tin (Sn).
17. The composite magnetic body according to claim 16, wherein the
metal element content is 0.1% to 90% by weight in the magnetic
powder.
18. The composite magnetic body according to claim 14, wherein the
material of the metal oxide magnetic powder is at least one
selected from the group consisting of goethite (FeOOH), hematite
(Fe.sub.2O.sub.3), magnetite (Fe.sub.3O.sub.4), manganese (Mn)-zinc
(Zn) ferrite, nickel (Ni)-zinc (Zn) ferrite, cobalt (Co) ferrite,
manganese (Mn) ferrite, nickel (Ni) ferrite, copper (Cu) ferrite,
zinc (Zn) ferrite, magnesium (Mg) ferrite, lithium (Li) ferrite,
manganese (Mn)-magnesium (Mg) ferrite, copper (Cu)-zinc (Zn)
ferrite, and manganese (Mn)-zinc (Zn) ferrite.
19. The composite magnetic body according to claim 1, wherein the
insulating material is a synthetic resin or liquid phase resin
containing at least one selected from the group consisting of
polyimide resin, polybenzoxazole resin, polyphenylene resin,
polybenzocyclobutene resin, polyarylene ether resin, polysiloxane
resin, epoxy resin, polyester resin, fluorocarbon polymer,
polyolefin resin, polycycloolefin resin, cyanate resin,
polyphenylene ether resin, and polystyrene resin; or at least one
ceramic raw material selected from the group consisting of
Al.sub.2O.sub.3, SiO.sub.2, TiO.sub.2, 2MgO.SiO.sub.2, MgTiO.sub.3,
CaTiO.sub.3, SrTiO.sub.3, and BaTiO.sub.3.
20. A method of manufacturing a composite magnetic body comprising
the steps of preparing a slurry by dispersing an insulating
material and a spherical or elliptic magnetic powder in a solvent
to mix and of applying the slurry, followed by drying and firing,
wherein the step of preparing the slurry includes the steps of
preparing a dispersion solvent by adding a surfactant in a solvent
and of mixing the magnetic powder to the dispersion solvent, and
the step of mixing the magnetic powder includes the steps of adding
a dispersive medium and of performing rotation/revolution
mixing.
21. The method of manufacturing a composite magnetic body according
to claim 20, wherein the rotation/revolution mixing is performed at
a rotation speed of 100 rpm or more and a revolution speed of 100
rpm or more.
22. The method according to claim 20, wherein the step of preparing
the slurry further includes the steps of adding an insulating
material to the slurry, followed by mixing, and of removing the
dispersive medium from the slurry before or after adding the
insulating material.
23. The method according to claim 22, wherein the step of removing
the dispersive medium includes the step of dividing the mixture
into a portion containing the dispersive medium and a portion not
containing the dispersive medium by allowing the mixture to stand,
or by centrifugating the mixture.
24. The method according to claim 20, wherein the material of the
magnetic powder is one selected from the group consisting of nickel
(Ni), Permalloy (Fe--Ni alloy), and Permalloy (Fe--Ni alloy)
containing at least one metal element selected from the group
consisting of aluminum (Al), chromium (Cr), manganese (Mn), cobalt
(co), copper (Cu), zinc (Zn), niobium (Nb), molybdenum (Mo), indium
(In), and tin (Sn).
25. The method according to claim 20, wherein the magnetic powder
is an iron-based magnetic powder or a metal oxide powder.
26. The method according to claim 25, wherein the material of the
iron-based metal magnetic powder is at least one selected from the
group consisting of iron (Fe), iron (Fe)-silicon (Si)-based alloy,
iron (Fe)-nitrogen (N)-based alloy, iron (Fe)-carbon (C)-based
alloy, iron (Fe)-boron (B)-based alloy, iron (Fe)-phosphorus
(P)-based alloy, iron (Fe)-aluminum (Al)-based alloy, and iron
(Fe)-aluminum (Al)-silicon (Si)-based alloy.
27. The method according to claim 26, wherein the material of the
iron-based metal magnetic powder contains at least one metal
element selected from the group consisting of titanium (Ti),
vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), copper
(Cu), zinc (Zn), niobium (Nb), molybdenum (Mo), indium (In), and
tin (Sn).
28. The method according to claim 25, wherein the material of the
metal oxide magnetic powder is at least one selected from the group
consisting of goethite (FeOOH), hematite (Fe.sub.2O.sub.3),
magnetite (Fe.sub.3O.sub.4), manganese (Mn)-zinc (Zn) ferrite,
nickel (Ni)-zinc (Zn) ferrite, cobalt (Co) ferrite, manganese (Mn)
ferrite, nickel (Ni) ferrite, copper (Cu) ferrite, zinc (Zn)
ferrite, magnesium (Mg) ferrite, lithium (Li) ferrite, manganese
(Mn)-magnesium (Mg) ferrite, copper (Cu)-zinc (Zn) ferrite, and
manganese (Mn)-zinc (Zn) ferrite.
29. The method according to claim 20, wherein the insulating
material is a synthetic resin or liquid phase resin containing at
least one selected from the group consisting of polyimide resin,
polybenzoxazole resin, polyphenylene resin, polybenzocyclobutene
resin, polyarylene ether resin, polysiloxane resin, epoxy resin,
polyester resin, fluorocarbon polymer, polyolefin resin,
polycycloolefin resin, cyanate resin, polyphenylene ether resin,
and polystyrene resin; or at least one ceramic raw material
selected from the group consisting of Al.sub.2O.sub.3, SiO.sub.2,
TiO.sub.2, 2MgO.SiO.sub.2, MgTiO.sub.3, CaTiO.sub.3, SrTiO.sub.3,
and BaTiO.sub.3.
30. The method according to claim 20, wherein the spherical
magnetic powder is mechanically deformed into an elliptic shape in
the step of mixing the magnetic powder to the dispersion
solvent.
31. The method according to claim 20, wherein the dispersive medium
added in the step of mixing the magnetic powder is a grain of at
least one type selected from the group consisting of metals, metal
oxides, sintered oxides, sintered nitrides, sintered silicides, and
glass.
32. The method according to claim 31, wherein the dispersive medium
contains at least one selected from the group consisting of
aluminum, steel, lead, iron oxides, alumina, zirconia, silicon
dioxide, titania, silicon nitride, silicon carbide, soda glass,
lead glass, and high-specific gravity glass.
33. The method according to claim 31, wherein the dispersive medium
has a specific gravity of 6 or more.
34. The method according to claim 33, wherein the dispersive medium
contains any one of zirconia, steel, and stainless steel.
35. The method according to claim 20, wherein the dispersive medium
is a grain having an average grin size in the range of 0.1 to 3.0
mm.
36. A circuit board comprising the composite magnetic body
according to claim 1.
37. An electronic apparatus comprising the circuit board according
to claim 36.
38. An electronic component comprising the composite magnetic body
according to claim 1.
39. An electronic apparatus comprising the electronic component
according to claim 38.
40. A circuit board comprising a composite magnetic body
manufactured by the method according to claim 20.
41. An electronic apparatus comprising the circuit board according
to claim 40.
42. An electronic component comprising a composite magnetic body
manufactured by the method according to claim 20.
43. An electronic apparatus comprising the electronic component
according to claim 42.
Description
TECHNICAL FIELD
[0001] The present invention relates to high-frequency circuit
boards and high-frequency electronic components, and particularly
to a composite magnetic body suitable for the high-frequency
circuit boards and high-frequency electronic components and a
method of manufacturing the composite magnetic body.
BACKGROUND ART
[0002] As the speed and the packing density of an information
communication apparatus are increased, it is strongly desired that
electronic components and circuit boards contained in an electronic
apparatus become smaller, and that their power consumptions are
reduced. The wavelength .lamda.g of electromagnetic waves
propagating in a material is generally expressed by the following
Equation 1, using the wavelength .lamda. of electromagnetic waves
propagating in a vacuum, and the relative permittivity .di-elect
cons.r and relative magnetic permeability .mu.r of the material. It
is thus known that as the relative permittivity Er and the relative
magnetic permeability .mu.r are increased, the electronic component
and circuit board can be miniaturized because the wavelength
shortening is increased.
.lamda.g=.lamda.0/(.di-elect cons.r.mu.r).sup.1/2 Equation 1
[0003] The characteristic impedance Zg of a material can be
expressed by the following Equation 2 using the vacuum
characteristic impedance Z0. For example, an approach has been
reported for reducing the power consumption of an electronic
component or a circuit board by increasing the relative magnetic
permeability .mu.r to increase the characteristic impedance Zg and
the terminating resistance, thus reducing the current running
through wires.
Zg=Z0(.mu.r/.di-elect cons.r).sup.1/2 Equation 2
[0004] However, an eddy current is generated at the surface of a
magnetic material at high frequencies that information
communication apparatuses or the like use. The eddy current is
produced in a direction in which the applied magnetic field is
canceled, and consequently reduces the apparent magnetic
permeability of the material. Also, the increase in eddy current
causes energy loss due to Joule's heat. It is therefore difficult
to use magnetic materials for circuit boards and electronic
components. In order to reduce the eddy current, it is more
effective to reduce the diameter of magnetic powder than to reduce
the skin depth d expressed by the following Equation 3.
d=1/(nf.mu.0.mu.r.nu.).sup.1/2 Equation 3
[0005] In the equation, f represents the signal frequency, .sigma.
represents the electric conductivity of magnetic powder, and .mu.0
represents the space permeability.
[0006] As the nanotechnology progresses, magnetic particles become
finer, and some cases have been reported in which the decrease in
relative magnetic permeability .mu.r of a material was prevented at
a high frequency.
[0007] Patent Document 1 discloses that an electromagnetic wave
absorber exhibiting superior radio wave absorption can be produced
by dispersing an elliptic nanocrystalline magnetic powder in a
resin to increase the imaginary part .mu.'' of magnetic
permeability, which is the magnetic loss term of the magnetic
permeability expressed on a complex permeability basis.
[0008] Patent Document 2 provides a composite magnetic body
exhibiting a low loss at about 300 MHz or less by dispersing
magnetic particles having a plurality of particle sizes in a resin
by dispersive mixing using screw stirring and ultrasonic
agitation.
[0009] In Japanese Patent Application No. 2007-12092, the inventors
of the present invention provide a composite magnetic body
exhibiting a relative magnetic permeability .mu.r of more than 1
and a loss tangent tan .delta. of 0.1 or less at frequencies of 500
MHz to 1 GHZ by appropriately dispersing spherical magnetic powder
or elliptic magnetic powder in a resin by a rotation/revolution
mixing using a dispersive medium.
[0010] Patent Document 1: JP-A-H11-354973
[0011] Patent Document 2: JP-A-2006-269134
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0012] Patent Document 1 discloses that an electromagnetic wave
absorber exhibiting superior radio absorption over a wide range of
frequencies can be produced by compounding an elliptic
nanocrystalline magnetic powder with a resin. However, Patent
Document 1 does not describe the process for dispersing magnetic
particles in detail. Also, in order to interrupt or absorb
electromagnetic waves, Patent Document 1 proposes a material having
a large imaginary part .mu.'' of magnetic permeability, which is
the magnetic loss term, at working frequencies.
[0013] Unfortunately, materials exhibiting high magnetic losses
cannot be used in applications requiring low magnetic loss, such as
for circuit boards or electronic components.
[0014] On the other hand, Patent Document 2 discloses a composite
magnetic body exhibiting low power consumption, capable of reducing
the crosstalk and radiation noise, and therefore suitable for
circuit boards and electronic components. In use of the spherical
magnetic powder disclosed as in patent Document 2, however, the
demagnetizing factor of each particle is increased, and accordingly
the relative magnetic permeability .mu.r is reduced. In this
instance, in order to increase the relative magnetic permeability
.mu.r, the mixture concentration must be increased. However, a high
mixture concentration tends to result in difficulty in manufacture,
and, for example, makes it difficult to obtain uniform
dispersion.
[0015] Furthermore, fine magnetic particles exhibit magnetic
interaction in addition to electric double layer interaction and
Van Der Waals attraction energy. Accordingly, such magnetic
particles easily come together to form an aggregate. The aggregate
of fine magnetic particles in a composite magnetic body acts as a
large magnetic particle, and easily generate an eddy current at
high frequencies to reduce the magnetic characteristics.
Accordingly, screw stirring, ultrasonic agitation or the like is
performed to prevent the magnetic particles from forming an
aggregate in the manufacture of the composite magnetic body.
[0016] However, it has been found that the mixing method disclosed
in patent Document 2 does not uniformly disperse the magnetic
particles in an insulating material because the energy externally
applied to the aggregate is lower than the energy forming the
aggregate, and consequently that the magnetic loss cannot be
sufficiently reduced at frequencies in the range of several
hundreds of megahertz to several gigahertz. Hence, it has been
found that the mixing method disclosed in Patent Document 2 cannot
sufficiently pulverize the aggregate.
[0017] In addition, since the magnetic powder contains magnetic
particles having a plurality of particle sizes, it is necessary not
only to select the type of magnetic powder, but also to select the
particle size of the magnetic powder. This disadvantageously
complicates the manufacturing process.
[0018] If the magnetic powder is a metal magnetic powder, the
saturation magnetization and the magnetic permeability are high,
but the electric resistivity is low (10.sup.-6 to 10.sup.-4
.OMEGA.cm). Accordingly, the metal magnetic powder increases the
eddy current loss to degrade the magnetic characteristics in a high
frequency region, as described above. The magnetic powder requires
dispersing uniformly in a composite magnetic body. The use of an
iron-based metal magnetic powder allows safer, more efficient and
lower cost manufacture on an industrial scale than the use of
nickel- or cobalt-based metal magnetic powder. If a metal oxide
magnetic powder is used, on the other hand, the electric
resistivity is higher (1 to 10.sup.8 .OMEGA.cm) than that of the
metal magnetic material. Accordingly, the eddy current loss is
reduced at high frequencies, and the magnetic characteristics are
not degraded much. However, the magnetic powder must be added to
the composite magnetic body at a high concentration because the
saturation flux density is 1/3 to 1/2 times that of metal magnetic
materials.
[0019] The inventors found in Japanese Patent Application No.
2007-12092 that by appropriately dispersing a magnetic powder, the
loss can be reduced even at frequencies in the range of 500 MHz to
1 GHz. However, 78-Permalloy (78Ni-22Fe alloy) constituting the
composite magnetic body cannot sufficiently avoid the influence of
the diamagnetic field because of its low plastic deformation
ability, and it is difficult to allow the high-frequency magnetic
field to coincide with the axis of easy magnetization because of
its low degree of crystal orientation. This hinders further
increase of magnetic permeability.
[0020] Accordingly, it is a first object of the present invention
to provide a composite magnetic body produced by dispersing a
magnetic powder in an insulating material, wherein the magnetic
powder has a spherical or elliptic shape, and the composite
magnetic body has a relative magnetic permeability pr of more than
1 and a loss tangent tan .delta. of 0.1 or less at a frequency of I
GHz.
[0021] It is a second object of the present invention to provide a
composite magnetic body containing a magnetic powder easily
plastic-deformed in the direction of a specific crystal orientation
(herein the direction of axis of easy magnetization) by adding a
metal element to alloy particles and applying a mechanical stress
to the alloy particles, and an insulating material, wherein the
longer axis direction of the elliptic magnetic powder coincides
with the direction of axis of easy magnetization of the elliptic
magnetic powder, and the composition magnetic material has a
relative magnetic permeability .mu.r of more than 10 and a loss
tangent tan .delta. of 0.3 or less at frequencies of 1.2 GHz or
less.
[0022] It is a third object of the present invention is to provide
a composite magnetic body that can exhibit a sufficiently low
magnetic loss at frequencies in the range of several hundreds of
megahertz to several gigahertz by use of either a metal magnetic
powder or a metal oxide magnetic powder.
[0023] It is a fourth object of the present invention is to provide
a method of producing any one of the above composite magnetic
bodies.
[0024] It is a fifth object of the present invention is to provide
a circuit board, an electronic component and an electronic
apparatus including any one of the above composite magnetic
bodies.
Means for Solving the Problems
[0025] As a result of intensive research, the present inventors
have found that the loss can be reduced even at frequencies in the
range of several hundreds of megahertz to several gigahertz by
appropriately dispersing a magnetic powder, and that the magnetic
permeability can further be increased at frequencies of 1.2 GHz or
less by appropriately dispersing an elliptic magnetic powder and
aligning the orientation of the elliptic magnetic powder.
[0026] That is, according to a first aspect of the present
invention, there is provided a composite magnetic body which
includes a magnetic powder dispersed in an insulating material. The
magnetic powder is in a spherical shape or an elliptic shape. In
the composite magnetic body, the composite magnetic body has any
one of the following characteristics (a) to (c):
[0027] (a) the relative magnetic permeability .mu.r is larger than
1 and the loss tangent tan .delta. is 0.1 or less, at a frequency
of 1 GHz or 500 MHz;
[0028] (b) the real part .mu.r' of the complex permeability is more
than 10 and the loss tangent tan .delta. is 0.3 or less, at a
frequency of 1.2 GHz or less; and
[0029] (c) the real part .mu.r' of the complex permeability is more
than 1 at a frequency of 4 GHz or less, and the loss tangent tan
.delta. is 0.1 or less at a frequency of 1 GHz or less.
[0030] In the above-mentioned aspect of the present invention, It
is preferable that the real part .di-elect cons.r' of the complex
permittivity of the composite magnetic body is 10 or more at a
frequency of 1 GHz or less or that the real part .di-elect cons.r'
of the complex permittivity of the composite magnetic body is 10 or
less at a frequency of 1 GHz or less.
[0031] In addition, according to a second aspect of the present
invention, there is provided a method of manufacturing a composite
magnetic body which includes the steps of preparing a slurry by
dispersing an insulating material and a spherical or elliptic
magnetic powder in a solvent to mix and of applying the slurry,
followed by drying and firing. In the method, the step of preparing
the slurry includes the steps of preparing a dispersion solvent by
adding a surfactant in a solvent and of mixing the magnetic powder
to the dispersion solvent. The step of mixing the magnetic powder
includes the steps of adding a dispersive medium and performing
rotation/revolution mixing.
[0032] In the above-mentioned aspect of the present invention, it
is preferable that the rotation/revolution mixing is performed at a
rotation speed of 100 rpm or more and a revolution speed of 100 rpm
or more. It is more preferable that the rotation/revolution mixing
is performed at a rotation speed of 500 rpm or more and a
revolution speed of 200 rpm or more.
[0033] According to a third aspect of the present invention, there
is provided a circuit board which includes the composite magnetic
body as described above and an electronic apparatus which includes
the circuit board.
[0034] According to a fourth aspect of the present invention, there
is provided an electronic component which includes the composite
magnetic body as described above.
[0035] According to a fifth aspect of the present invention, there
is provided an electronic apparatus which includes the electronic
component as described above.
[0036] According to a sixth aspect of the present invention, there
is provided a circuit board which includes a composite magnetic
body manufactured by the method as described above.
[0037] According to a seventh aspect of the present invention,
there is provided an electronic apparatus which includes the
circuit board as described above.
[0038] According to an eighth aspect of the present invention,
there is provided an electronic component which includes a
composite magnetic body manufactured by the method as described
above.
[0039] According to a ninth aspect of the present invention, there
is provided an electronic apparatus which includes the electronic
component as described above.
ADVANTAGES
[0040] According to the present invention, by appropriately
dispersing spherical or elliptic magnetic powder in a insulating
material, a composite magnetic body having a relative magnetic
permeability .mu.r of higher than 1 and a loss tangent tan .delta.
of 0.1 or less at a frequency of 1 GHz. By using the composite
magnetic body according to the present invention as the material of
a circuit board and/or an electronic component, a miniaturized
low-power consumption information communication apparatus used at
frequencies in the range of several hundreds of megahertz to
several gigahertz can be achieved, which is not easily achieved by
use of a circuit board or electronic component made of only a
dielectric material.
[0041] The present invention can also provide a composite magnetic
body containing an insulating material and a magnetic powder
containing a metal element that can be easily plastic-deformed in
the direction of a specific crystal orientation (for example, the
direction of axis of easy magnetization) by applying a mechanical
stress, and an electronic apparatus using the same. The
longitudinal direction of the elliptic magnetic powder coincides
with the axis of easy magnetization of the elliptic magnetic
powder, and the composition magnetic material has a relative
magnetic permeability .mu.r of more than 10 and a loss tangent tan
.delta. of 0.3 or less at frequencies of 1.2 GHz or less. By using
the composite magnetic body having a high magnetic permeability
according to the present invention as the material of a circuit
board and/or an electronic component, a miniaturized low-power
consumption information communication apparatus used at frequencies
in the range of several hundreds of megahertz to 1 GHz can be
achieved.
[0042] According to the present invention, by appropriately
dispersing a magnetic power containing an iron-based magnetic
powder or metal oxide magnetic powder in an insulating material by
mixing, a composite magnetic body can be achieved which has a
relative magnetic permeability .mu.r of higher than 1 at
frequencies of 4 GHz or less, and a loss tangent tan .beta. of 0.1
or less at frequencies of 1 GHz or less. By using the composite
magnetic body according to the present invention as the material of
a circuit board and/or an electronic component, a miniaturized
low-power consumption information communication apparatus used at
frequencies in the range of several hundreds of megahertz to
several gigahertz can be achieved, which is not easily achieved by
use of a circuit board or electronic component made of only a
dielectric material.
BRIEF DESCRIPTION OF DRAWINGS
[0043] FIG. 1 is a graph showing the magnetic characteristics of a
composite magnetic body prepared in Example 1 of the present
invention plotted versus frequency.
[0044] FIG. 2 is a scanning electron microphotograph of the
composite magnetic body prepared in Example 1 of the present
invention.
[0045] FIG. 3 is a graph showing the magnetic characteristics of a
composite magnetic body prepared in Example 2 of the present
invention plotted versus frequency.
[0046] FIG. 4 is a scanning electron microphotograph of the
composite magnetic body prepared in Example 2 of the present
invention.
[0047] FIG. 5 is a graph showing the magnetic characteristics of a
composite magnetic body prepared in a known method plotted versus
frequency.
[0048] FIG. 6 is a scanning electron microphotograph of the
composite magnetic body prepared in the known method.
[0049] FIG. 7 is a schematic view of the structure of a
high-frequency circuit board according to Example 3 of the present
invention.
[0050] FIG. 8 is a graph showing the transmission characteristic
and the reflection characteristic of the high-frequency circuit
board shown in FIG. 7 plotted versus frequency.
[0051] FIG. 9 is a schematic view of the structure of an antenna
according to Example 4 of the present invention.
[0052] FIG. 10 is a graph showing the input reflection
characteristic of the antenna shown in FIG. 9 plotted versus
frequency.
[0053] FIG. 11 is a graph showing the magnetic characteristics of a
composite magnetic body prepared in Example 5 of the present
invention plotted versus frequency.
[0054] FIG. 12 is a scanning electron microphotograph of the
composite magnetic body prepared in Example 5 of the present
invention.
[0055] FIG. 13 is a graph showing the result of X-ray diffraction
of the composite magnetic body prepared in Example 5 of the present
invention.
[0056] FIG. 14 is a graph showing the magnetic characteristics of a
composite magnetic body prepared in a known method plotted versus
frequency.
[0057] FIG. 15 is a scanning electron microphotograph of the
composite magnetic body prepared in the known method.
[0058] FIG. 16 is the result of X-ray diffraction of the composite
magnetic body prepared in a known method.
[0059] FIG. 17 is a schematic view of the structure of an antenna
prepared in Example 6 of the present invention.
[0060] FIG. 18 is a graph showing the input reflection
characteristic of an antenna plotted versus frequency.
[0061] FIG. 19 is a graph showing the magnetic characteristic of a
composite magnetic body prepared in Example 7 of the present
invention plotted versus frequency.
[0062] FIG. 20 is a scanning electron microphotograph of the
composite magnetic body prepared in Example 7 of the present
invention.
[0063] FIG. 21 is a graph showing the magnetic characteristic of a
composite magnetic body prepared in Example 8 of the present
invention plotted versus frequency.
[0064] FIG. 22 is a scanning electron microphotograph of a
composite magnetic body prepared in Example 8 of the present
invention.
REFERENCE NUMERALS
[0065] 10 composite magnetic substrate [0066] 12 conductor line
[0067] 14 feed port [0068] 16 composite magnetic antenna [0069] 20
composite magnetic body [0070] 22 strip conductor [0071] 24
conductor plate [0072] 26 feeding point
BEST MODES FOR CARRYING OUT THE INVENTION
[0073] A magnetic powder constituting a composite magnetic body
according to an embodiment of the present invention will first be
described.
[0074] The material of the magnetic powder may be at least one
metal selected from the group consisting of iron (Fe), cobalt (Co)
and nickel (Ni), or an alloy or compound of the metal. Preferably,
the material of the magnetic powder is selected from iron or
iron-based alloy prepared by adding at least one metal element
selected from the group including titanium (Ti), aluminum (Al),
chromium (Cr), manganese (Mn), cobalt (Co), copper (Cu), zinc (Zn),
niobium (Nb), molybdenum (Mo), vanadium (V), indium (In) and tin
(Sn) into iron or iron-based alloy having a high saturation
magnetization, such as iron (Fe), Permalloy (Fe--Ni alloy),
Supermalloy (Fe--Ni--Mo alloy), Sendust (Fe--Si--At alloy), Fe--Si
alloy, Fe--Co-based alloy, Fe--Cr alloy, Fe--Cr--Si alloy, iron
(Fe)-nitrogen (N)-based alloy, iron (Fe)-carbon (C)-based alloy,
iron (Fe)-boron (B)-based alloy, iron (Fe)-phosphorus (P)-based
alloy, iron (Fe)-aluminum (Al), or the like. The magnetic powder
prepared by adding such a metal element to iron or an iron-based
alloy becomes soft and its plastic deformation ability is enhanced.
Accordingly, the magnetic powder is easily plastic-deformed by
applying a mechanical stress, and an elliptic magnetic powder
having a high aspect ratio can readily be produced. In addition,
since the longitudinal direction of the elliptic magnetic powder
coincides with the axis of easy magnetization, the magnetic
permeability of the composite magnetic body can be enhanced.
[0075] Preferably, the metal element content is in the range of
0.1% to 90% by weight. This is because less than 0.1% by weight of
the metal element does not allow sufficient plastic deformation of
the soft magnetic powder, and because more than 90% by weight of
the metal element results in a reduced saturation magnetization of
the magnetic powder due to a small magnetic moment of the metal
element.
[0076] Ferrite compounds having high electric resistivities are
also preferred, such as magnetite (Fe.sub.3O.sub.4), manganese
(Mn)-zinc (Zn) ferrite, nickel (Ni)-zinc (Zn) ferrite, cobalt (Co)
ferrite, manganese (Mn) ferrite, nickel (Ni) ferrite, copper (Cu)
ferrite, zinc (Zn) ferrite, magnesium (Mg) ferrite, lithium (Li)
ferrite, manganese (Mn)-magnesium (Mg) ferrite, copper (Cu)-zinc
(Zn) ferrite, and manganese (Mn)-zinc (Zn) ferrite.
[0077] Preferably, the magnetic powder content in the composite
magnetic body is in the range of 10% to 95% by volume, preferably
10% by volume or more, and particularly preferably in the range of
10% to 90% by volume. Ten percent by volume of magnetic powder is
too small to obtain a high relative magnetic permeability .mu.r. In
contrast, as the magnetic powder content is increased, it becomes
difficult to coat the composite magnetic body. In particular, more
than 95% by volume of magnetic powder accounts for such a high
proportion in the composite magnetic body that a coating of the
insulating material cannot be formed, and an aggregate is formed to
increase the loss tangent tan .delta..
[0078] The magnetic powder containing the above-described material
may be in a spherical or elliptic shape, and preferably has a
particle size in the range of 0.01 to 10 .mu.m. The reason why the
range of 0.01 to 10 .mu.m is preferred is that the particle size of
the magnetic powder has a close connection with the saturation
magnetization. If the particle size is reduced, some changes occur,
such as increase in number of particles, decrease in volume per
particle, and increase in total area. The increase in total area
more than in volume means that the property in which the surface is
involved is dominated by the particles. In general, the surface
layer has a different composition and structure from the interior.
If the particle size is reduced, atoms involved in the magnetic
characteristics are relatively reduced to reduce the saturation
magnetization. Accordingly, a particle size of at least 0.01 .mu.m
or more is required. Also, since excessively large particles cause
an eddy current at high frequencies, the upper limit of the average
particle size is 10 .mu.m.
[0079] The elliptic magnetic powder is formed by mechanically
deforming the spherical magnetic powder by the shearing stress of
the dispersive medium during mixing the magnetic powder in a
dispersion solvent, and preferably has thickness of 0.1 to 1 .mu.m.
It is difficult to form an elliptic magnetic powder having a
thickness of less than 0.1 .mu.m, and such an elliptic magnetic
powder is difficult to handle. In contrast, an elliptic magnetic
powder having a thickness of more than 1 .mu.m undesirably causes
an eddy current to degrade the magnetic characteristics at high
frequencies. In addition, if the elliptic magnetic powder has an
aspect ratio (length/thickness) of less than 2, the demagnetizing
factor of the powder is undesirably increased to reduce the
relative magnetic permeability of the composite magnetic body.
[0080] The insulating material contained in the composite magnetic
body will now be described.
[0081] If the composite magnetic body is used for a circuit board,
the permittivity is preferably low from the viewpoint of increasing
the characteristic impedance. Accordingly, the insulating material
is preferably selected from synthetic resins having low
permittivities, such as polyimide resin, polybenzoxazole resin,
polyphenylene resin, polybenzocyclobutene resin, polyarylene ether
resin, polysiloxane resin, epoxy resin, polyester resin,
fluorocarbon polymer, polyolefin resin, polycycloolefin resin,
cyanate resin, polyphenylene ether resin, and polystyrene
resin.
[0082] If a high permittivity is required as in the use for a
capacitor or an antenna element, a ceramic, such as
Al.sub.2O.sub.3, SiO.sub.2, TiO.sub.2, 2Mg.SiO.sub.2, MgTiO.sub.3,
CaTiO.sub.3, SrTiO.sub.3 or BaTiO.sub.3, or a mixture of these
inorganic materials and an organic material may be used as
required.
[0083] Now, description will be made as regards a method of
manufacturing the composite magnetic body according to an
embodiment of the present invention.
[0084] For comparative evaluation, first, the known method
disclosed in Patent Document 2 by the present inventors was
examined. One gram of 78-Permalloy magnetic powder (Ni:78%-Fe:22%
alloy) having an average particle size of 0.15 .mu.m and a
dispersion liquid prepared by dissolving a nitrogen-containing
graft polymer as a surfactant in 10 g of 4:1 xylene-cyclopentanone
mixed solution were mixed by rotation/revolution stirring and
ultrasonic irradiation agitation, thus preparing a slurry. The
slurry and 0.5 g of resin varnish prepared by diluting a
polycycloolefin resin to a solid content of 40% were mixed by
rotation/revolution stirring and ultrasonic irradiation agitation.
The resulting paste was subjected to concentration, application,
drying, heat treatment and press forming to complete a composite
magnetic body. The complex permeability of the resulting composite
magnetic body was measured by a parallel line method, and resulted
in a relative magnetic permeability .mu.r of 4 and a magnetic loss
tan .delta. of 0.3 at a frequency of 1 GHz. It was found that while
superior magnetic characteristics were exhibited up to a frequency
of about 200 to 300 MHz, the magnetic loss was increased at
frequencies of 300 MHz or more (see FIG. 5). The dispersibility of
the magnetic powder in a sheet of the composite magnetic body was
observed through a scanning electron microscope. It was found that
spherical particles had come together to form an aggregate of about
1 .mu.m or more (see FIG. 6).
[0085] Accordingly, the present inventors have conducted intensive
research, and have found that a composite magnetic body exhibiting
a relative magnetic permeability .mu.r of 1 or more and a loss
tangent tan .delta. of 0.1 or less at frequencies of 1 GHz or less
can be produced by mixing in the following manufacturing
method.
[0086] The greatest feature of the production method according to
the present invention is that iron or iron-based alloy having a
high saturation magnetization, or a ferrite compound having a high
electric resistivity is mixed with an insulating material in a
solvent in a mixing vessel containing a dispersive medium by
rotation/revolution stirring at a high speed (a rotation speed of
100 rpm or more and a revolution speed of 100 rpm or more,
preferably a rotation speed of 500 rpm or more and a revolution
speed of 200 rpm or more). The dispersive medium produces a high
shearing stress to deform the magnetic particles into an elliptic
shape or pulverize the aggregate of the particles. Thus, the
dispersibility of the magnetic powder is increased, and the
magnetic powder can be present uniformly at a high concentration in
the composite magnetic body.
[0087] More specifically, the manufacturing method according to the
present invention includes the step of preparing a slurry by
dispersing a magnetic powder or a magnetic powder containing a
metal element in a solvent. This step includes the step of
preparing a dispersion solvent by adding a surfactant in the
solvent, and the mixing step of mixing the magnetic powder to the
dispersion solvent. For mixing the magnetic powder to the
dispersion solvent, a dispersive medium is added, and
rotation/revolution mixing was performed with the dispersive medium
contained. Thus, the magnetic powder plastic-deformed in the
direction of a specific crystal plane orientation is deformed into
an elliptic shape by a mechanical stress produced by the dispersive
medium, and then an insulating material is added.
[0088] Thus, a slurry containing a solvent, a surfactant, a
magnetic powder, a dispersive medium and an insulating material is
prepared. After the rotation/revolution mixing, the dispersive
medium is removed from the resulting mixture. The step of removing
the dispersive medium may be performed before adding and mixing the
insulating material. For removing the dispersive medium, the
mixture may be allowed to stand until the dispersive medium is
separated from the solvent and other constituent, or the mixture
may be subjected to centrifugation to separate the dispersive
medium from the mixture.
[0089] Apparatuses that can be used in the above mixing step of
mixing the solvent, the surfactant, the magnetic powder, the
dispersive medium and the insulating material include kneaders,
roll mills, pin mills, sand mills, ball mills and planet ball
mills. In use of the dispersive medium of the invention, sand
mills, ball mills or planet ball mills are suitable.
[0090] Dispersive media include metals or metal oxides of aluminum,
steel, lead or the like, sintered oxides such as alumina, zirconia,
silicon dioxide and titania, sintered nitrides such as silicon
nitride, sintered silicides such as silicon carbide, and glasses
such as soda glass, lead glass and high-specific gravity glass.
From the viewpoint of mixing efficiency, the dispersive medium is
preferably zirconia, steel or stainless steel, having a specific
gravity of 6 or more. The dispersive medium features a higher
hardness than the magnetic powder.
[0091] Since the mixing is performed by impact produced by
collision with the dispersive medium, the dispersibility is
increased as the number of collisions is increased. As the average
grain size of the dispersive medium is reduced, the number of
grains packed in a unit volume is increased, and the number of
collisions is increased to increase the dispersibility,
accordingly. However, a medium having an excessively small grain
size is difficult to separate from the slurry. Accordingly, a grain
size of at least 0.1 mm or more is required. In contrast, a
dispersive medium having an excessively large grain size results in
reduced collisions and reduced dispersibility. Thus, the upper
limit of the average grain size is 3.0 mm.
[0092] If the mixing and agitation time is too short, the spherical
magnetic particles cannot be sufficiently deformed into an elliptic
shape. If the mixing and agitation time is too long, the deformed
elliptic magnetic particles are then pulverized. Consequently, an
appropriate aspect ratio (length/thickness) cannot be maintained,
and the magnetic characteristics are degraded at high frequencies.
Accordingly, the mixing and agitation time is preferably about 30
minutes, and is appropriately controlled by adjusting the amounts
of raw materials to be initially introduced and the rotation and
revolution speeds for agitation.
[0093] The application method of the resulting slurry will now be
described. The slurry may be formed into a sheet by any known
forming technique, such as press, doctor blade method or injection
molding, thus forming a dry film. From the viewpoint of forming a
multilayer composite of the composite magnetic body, a doctor blade
method is preferably selected among these methods to form a sheet.
The slurry is concentrated by evaporating the solvent to adjust the
viscosity so as to be suitable for the application method. After
the application of the slurry, the elliptic magnetic powder is
aligned in the direction parallel to the sheet by a magnetic field,
if necessary, before drying. Then the elliptic particles are
aligned in the direction parallel to the surface of the sheet. At
this time, the axis of easy magnetization in the elliptic particles
is oriented in the direction of the longer axis of the elliptic
particles. Consequently, the shape anisotropy and the crystal
anisotropy are simultaneously aligned.
[0094] Finally, the thus formed dry film is subjected to heat
treatment and press forming in a reducing atmosphere or in a
vacuum, and thus the composite magnetic body is completed.
[0095] The greatest feature of the present invention is that the
elliptic magnetic powder constituting the composite magnetic body
is easy to plastic-deform in the direction of a specific crystal
orientation (in the direction of the axis of easy magnetization,
here), is easily plastic-deformed by applying a mechanical stress,
has a high aspect ratio, and is arranged (aligned) in a direction
parallel to a specific direction by applying an external
magnetization for manufacturing the composite magnetic body.
Accordingly, the magnetic permeability of the composite magnetic
body can be enhanced by reducing the demagnetizing factor in the
direction of the surface of the composite magnetic body and by
allowing the longitudinal direction of the elliptic magnetic powder
to coincide with the direction of the axis of easy
magnetization.
[0096] The manufacturing method of the present invention can reduce
the local aggregation of magnetic particles in the composite
magnetic body, and, thus, can achieve both the increase in relative
magnetic permeability .mu.r and the decrease in magnetic loss tan
.delta., at high frequencies.
[0097] The present invention will now be described in detail with
reference to Examples 1 to 8. However, the invention is not limited
to these Examples.
Example 1
[0098] One gram of 78-Permalloy magnetic powder (Ni:78%-Fe:22%
alloy) having an average particle size of 0.15 .mu.m was mixed to a
dispersion liquid prepared by dissolving a nitrogen-containing
graft polymer as a surfactant in 10 g of 4:1 xylene-cyclopentanone
mixed solution, and zirconia beads having an average grain size of
200 .mu.m were further added as the dispersive medium to the
mixture. The mixture in this state was subjected to planet stirring
for 30 minutes to deform the magnetic powder into an elliptic
shape. To the resulting slurry was added 0.5 g of resin varnish
prepared by diluting a polycycloolefin resin to a solid content of
40%, and then the slurry was further mixed by planet stirring for 5
minutes. Zirconia beads were further added as the dispersive
medium, and planet stirring was performed another five minutes. The
planet stirring was performed at a rotation speed of 2000 rpm and a
revolution speed of 800 rpm.
[0099] The resulting mixture was allowed to stand until the
dispersive medium was sedimented (while the magnetic powder has a
specific gravity of 7 to 8, zirconia has a specific gravity of 6 to
7. However, while the zirconia beads have a grain size of 200
.mu.m, the magnetic powder has a particle size of 0.15 .mu.m. Since
the zirconia beads are heavier than the magnetic powder, the
zirconia beads can sediment). The supernatant was placed in a
rotary evaporator, and the solvent was evaporated at 50.degree. C.
under a reduced pressure of 2.7 kPa (the boiling point of the
solvent is reduced by reducing the pressure) so that the viscosity
was adjusted so as to be suitable for application by a doctor blade
method. The resulting mixture was formed into a film by a doctor
blade method, and the film was dried a room temperature while a
magnetic field of 1.6.times.10.sup.5 A/m was applied to the film to
align the magnetic particles. The resulting dry film was subjected
to pressing firing in a vacuum press apparatus. For pressing, the
temperature was increased to 130.degree. C. over a period of 20
minutes under atmospheric pressure, and subsequently a pressure of
2 MPa was applied and held for 5 minutes. Then, the temperature was
increased to 160.degree. C. and held for 40 minutes. Thus, the
resin was cured to produce a composite magnetic body having an area
of 30 mm square and a thickness of about 60 .mu.m. The complex
permeability of the composite magnetic body was measured by a
parallel line method, and resulted in a relative magnetic
permeability .mu.r of 6 and a magnetic loss tan .delta. of 0.08 at
1 GHz (see FIG. 1). The structure of the composite magnetic body is
shown in the microphotograph of FIG. 2. It is shown that the
magnetic particles are in an elliptic shape and aligned in a
direction in which a magnetic field is applied.
Example 2
[0100] A composite magnetic body having an area of 30 mm square and
a thickness of 60 .mu.m was produced using 1 g of 45-Permalloy
magnetic powder (Ni:45%-Fe:55% alloy) having an average particle
size of 0.15 .mu.m under the same conditions as in Example 1. The
complex permeability of the composite magnetic body was measured by
a parallel line method, and resulted in a relative magnetic
permeability .mu.r of 5 and a magnetic loss tan .delta. of 0.05 at
1 GHz (see FIG. 3). The structure of the composite magnetic body is
shown in the microphotograph of FIG. 4.
Example 3
[0101] An example will be described in which the composite magnetic
body was used for a circuit board. First, 6 composite magnetic dry
films having a thickness of about 60 .mu.m prepared by the process
shown in Example 1 were stacked and subjected to pressing firing,
thus forming a composite magnetic material having a thickness of
about 350 .mu.m. Furthermore, the composite magnetic material was
sandwiched between low-permittivity resin films, and then heated to
cure the resin. Then, the surface of the resin was plated with
copper to form a wiring pattern (microstrip line) of 30 mm in
length and 0.9 mm in width. The external view of the circuit board
is shown in FIG. 7. FIG. 8 shows the transmission characteristic
and the reflection characteristic of the circuit board. The
measurement results favorably coincide with the calculation values
obtained by an electromagnetic field simulator HFSS, and thus it is
shown that a desired relative magnetic permeability and loss were
obtained at high frequencies.
Example 4
[0102] A case will now be described in which the composite magnetic
body was used as a mobile device antenna, which is an example of
electronic components. As shown in FIG. 9, an antenna element had a
structure in which a conductor line having a length of 44 mm and a
width of 1.5 mm was sandwiched between two composite magnetic
materials of 42 mm in length, 5 mm in width and 0.35 mm in
thickness. The antenna element was connected to a conductor plate
of 80 mm in length, 35 mm in width and 1 mm in thickness, and
50.OMEGA. was fed at a connection point. FIG. 10 shows the input
reflection characteristic of the antenna. The measurement results
favorably coincide with the calculation values obtained by an
electromagnetic field simulator HFSS, and thus it is shown that a
desired relative magnetic permeability and loss were obtained at
high frequencies.
Example 5
[0103] Two grams of Permalloy magnetic powder containing a metal
element and having an average particle size of 0.25 .mu.m was mixed
to a dispersion liquid prepared by dissolving a nitrogen-containing
graft polymer as a surfactant in 10 g of 4:1 xylene-cyclopentanone
mixed solution, and zirconia beads having an average grain size of
200 .mu.m were further added as the dispersive medium to the
mixture. The mixture in this state was subjected to planet stirring
for 50 minutes to deform the magnetic powder into an elliptic
shape. To the resulting slurry was added 0.5 g of resin varnish
prepared by diluting a polycycloolefin resin to a solid content of
40%, and then the slurry was further mixed by planet stirring for 5
minutes. The planet stirring was performed at a rotation speed of
2000 rpm and a revolution speed of 800 rpm.
[0104] The resulting mixture was allowed to stand until the
dispersive medium was sedimented (while the magnetic powder has a
specific gravity of 7 to 8, zirconia has a specific gravity of 6 to
7. However, while the zirconia beads have a grain size of 200
.mu.m, the magnetic powder has a particle size of 0.25 .mu.m. Since
the zirconia beads are heavier than the magnetic powder, the
zirconia beads can sediment). The supernatant was placed in a
rotary evaporator, and the solvent was evaporated at 50.degree. C.
under a reduced pressure of 2.7 kPa (the boiling point of the
solvent is reduced by reducing the pressure). After a film was
formed by a doctor blade method, the film was dried at room
temperature while a magnetic field of 1.6.times.10.sup.5 A/m was
applied to the film to align the magnetic particles. Six resulting
dry films were stacked and subjected to pressing firing in a vacuum
press apparatus. For pressing, the temperature was increased to
130.degree. C. over a period of 20 minutes under atmospheric
pressure, and subsequently a pressure of 2 MPa was applied and held
for 5 minutes. Then, the temperature was increased to 160.degree.
C. and held for 40 minutes. Thus, the resin was cured to produce a
composite magnetic material having a thickness of 350 .mu.m.
[0105] The particles of the magnetic powder in the resulting
magnetic material were finally deformed an elliptic shape in the
direction of axis of easy magnetization, and became in a state in
which their crystal planes parallel to the axis of easy
magnetization are piled in the thickness direction.
[0106] The complex permeability of this composite magnetic material
was measured by a parallel line method, and resulted in a relative
magnetic permeability .mu.r of 11 and a magnetic loss tan .delta.
of 0.25 at 1.2 GHz (see FIG. 11). Also, the permittivity was
measured by a parallel plate method, and resulted in a relative
permittivity of 12 and a dielectric loss tan .delta. of 0.05.
[0107] The structure photograph of the composite magnetic body is
shown in FIG. 12. It is shown that the magnetic particles are in an
elliptic shape and aligned in a specific direction. In this
instance, the elliptic particles measured about 0.03 .mu.m in
thickness and about 1 .mu.m in length on average, and thus the
aspect ratio was about 33. The results of X-ray diffraction shown
in FIG. 13 show that specific crystal planes are aligned. For
comparison, the magnetic permeability, the sectional photograph and
the X-ray diffraction results of a composite magnetic body prepared
by a known method without applying a direct-current magnetic field
are shown in FIGS. 14, 15 and 16, respectively. In this instance,
the elliptic particles were not aligned in a specific direction, or
orientation was not observed in crystal planes. As a result, it is
shown that the relative magnetic permeability was as low as about
7.
Example 6
[0108] A case will now be described in which the composite magnetic
body was used as a monopole antenna, which is an example of
electronic components. As shown in FIG. 17, an antenna element had
a structure in which a strip conductor 22 having a length of 55 mm
and a width of 1.5 mm was sandwiched between two composite magnetic
bodies 20 of 50 mm in length, 5 mm in width and 0.5 mm in
thickness. The antenna element was connected to the center of a 300
mm square conductor plate 24, and 50.OMEGA. was fed at a connection
point as a feeding point 26.
[0109] FIG. 18 shows the input reflection characteristics of the
antenna. The measurement results favorably coincide with the
calculation values obtained by inputting the material constants of
the composite magnetic body into an electromagnetic field simulator
HFSS. The resonance frequency of the composite magnetic body-loaded
antenna (indicated with "With MD" in FIG. 18) was compared with
that of a composite magnetic body-unloaded antenna (indicated with
"Without MD" in FIG. 18). As a result, the resonance frequency was
shifted from 1.26 GHz to 0.88 GHz by loading the composite magnetic
body 20. This shows that a greater wavelength compaction was
achieved because of the effects of the relative magnetic
permeability and relative permittivity of the composite magnetic
body, and that the antenna can be about 30% miniaturized.
Example 7
[0110] One gram of Fe magnetic powder having an average particle
size of 0.1 .mu.m was mixed to a dispersion liquid prepared by
dissolving a nitrogen-containing graft polymer as a surfactant in
10 g of 4:1 xylene-cyclopentanone mixed solution. The mixture was
subjected to planet stirring for 30 minutes using zirconia beads.
The planet stirring was performed at a rotation speed of 2000 rpm
and a revolution speed of 800 rpm. To the resulting slurry was
added 0.5 g of resin varnish prepared by diluting a polycycloolefin
resin to a solid content of 40%, and then the slurry was further
mixed by planet stirring for 5 minutes using zirconia beads.
[0111] Subsequently, the resulting mixture was placed in a rotary
evaporator, and the solvent was evaporated at 50.degree. C. under a
pressure of 2.7 kPa so that the viscosity was adjusted so as to be
suitable for application by a doctor blade method.
[0112] The resulting mixture was formed into a film by a doctor
blade method, and the film was dried at room temperature while a
magnetic field of 1.6.times.10.sup.5 A/m was applied to the film to
align the magnetic particles. The resulting dry film was subjected
to pressing firing in a vacuum press apparatus. For pressing, the
temperature was increased to 130.degree. C. over a period of 20
minutes under atmospheric pressure, and subsequently a pressure of
2 MPa was applied and held for 5 minutes. Then, the temperature was
increased to 160.degree. C. and held for 40 minutes. Thus, the
resin was cured to produce a composite magnetic body having an area
of 30 mm square and a thickness of about 60 .mu.m. The complex
permeability of the composite magnetic body was measured by a
parallel line method, and resulted in a relative magnetic
permeability or of 5 and a magnetic loss tan .delta. of 0.1 at 1
GHz (see FIG. 19). The structure photograph of the composite
magnetic body is shown in FIG. 20.
Example 8
[0113] A composite magnetic body having an area of 30 mm square and
a thickness of 60 .mu.m was produced using 1 g of magnetite
(Fe.sub.3O.sub.4) magnetic powder having an average particle size
of 0.1 .mu.m under the same conditions as in Example 1. The complex
permeability of the composite magnetic material was measured by a
parallel line method, and resulted in a relative magnetic
permeability .mu.r of 5 and a magnetic loss tan .delta. of 0.1 at 1
GHz (see FIG. 21). The structure photograph of the composite
magnetic body is shown in FIG. 22.
INDUSTRIAL APPLICABILITY
[0114] The present invention can be applied to semiconductor
devices, circuit elements, flat display devices, and other
high-frequency electronic components, and can also be applied to
high-frequency circuit boards including such components to reduce
the size and power consumption. Accordingly, the present invention
can reduce the size and power consumption of all high-frequency
electronic apparatuses including an electronic component and/or a
circuit board according to the present invention.
[0115] Furthermore, the composite magnetic body according to the
present invention can be used for an antenna to miniaturize the
antenna.
* * * * *